The construction of factory-made flexible HVAC ducts is well known in the industry. These types of ducts usually comprise a helical-supported duct liner (sometimes referred to as the core or inner core) covered by a layer of fiberglass insulation, which is, in turn, covered by a scrim-reinforced vapor barrier. Scrim is a material composed of geometrically-patterned cords that adds strength to a laminate construction when made a part thereof. U.S. Pat. Nos. 6,158,477 and 5,785,091 show typical constructions of factory made ducts. U.S. Pat. No. 5,785,091 teaches that the duct liner and vapor barrier can be manufactured from polymer tapes, particularly polyester. U.S. Pat. No. 5,526,849 discloses a plastic helix in combination with a metal helix and U.S. Pat. No. 4,990,143 discloses a polyester helix. United States Patent Publication No. 2007/0131299 discloses a polyester scrim used in a vapor barrier.
In the prior art, factory-made flexible HVAC ducts are typically constructed of three main components; a duct liner for conveying air, a layer of insulation for preventing energy loss through the duct wall, and a vapor barrier for holding the fiberglass around the liner while protecting the fiberglass from moisture. The duct liner is commonly constructed of a steel wire sandwiched between layers of polyester (PET) film. Other plastics and coated fabrics are also used to construct the wall of the duct liner. United States Published Patent Application No. 2010, 0186846 to Carlay et al. is another example of flexible duct and it is incorporated in its entirety herein.
In the HVAC industry, ductwork is often times specified by building codes to have a certain R value for a particular application. For example, if the ductwork is to run in an unconditioned space, the R value must be at least 6.0. The most common specified North American flexible duct fiberglass R-values are R4.2, R6.0 and R8.0 and each may be purchased pre-certified from fiberglass manufacturers. Obviously, the cost of the ductwork increases from one that has an R6.0 value to an R8.0 value due to the need to provide additional insulation, which is generally fiberglass insulation.
However, there is always a need to provide improved duct designs in the HVAC industry and other areas where air or fluid handling is necessary. The present invention responds to this need by providing an improved insulated duct.